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I took my vehicle to a shop in order to diagnose some severe driveability issues (it is a 96 G10 van with a 5.0 for reference). I was told that the fuel pressure was fine but the volume was "all over the place" once the van had warmed up.

The mechanic indicated that I need a fuel pump and filter. Now obviously I know the filter and pump are necessary for fuel delivery; however, I am a bit perplexed about what else might cause fuel volume issues. I have struggled to find information about fuel volume issues with fuel pressure being more widely covered. I would obviously expect a relationship between pressure and volume, but what could cause erratic fuel volume levels but acceptable pressure levels? In my case, according to shop, the fuel volume was problematic only after the van was warm, but, in general, what might be both the causes and symptoms of improper fuel volume levels? I personally would have expected a fault with one of the vehicle's electrical sensors, but this might be an misguided belief.

Thanks.

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    I've always assumed fuel pressure was the key to it running properly. If fuel volume wasn't enough to satisfy the needs of the engine, fuel pressure would drop ... at least that was my assumption. It would, at the very least, create problems with fuel pressure stability. Yes, fuel volume can create issues, but if there were really issues there, you'd also see problems in the fuel pressure. – Pᴀᴜʟsᴛᴇʀ2♦ Oct 13 '17 at 12:18
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    I don't believe this is a standard terminology. Possibly there is an issue with the mixture ratio and he tried to "dumb it down" for you. Go back and ask for a more clear explanation.. Are codes set? – agentp Oct 13 '17 at 12:18
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    You can have a restriction to the flow while the pressure is within limits - a blocked filter can exhibit this type of problem. – Solar Mike Oct 13 '17 at 12:20
  • @SolarMike - Pressure behind the blockage would be fine, but not after, at least while the vehicle was running. I'm wondering how the mechanic was measuring flow in the first place, especially accurately enough to suggest there'd be a problem (without taking the entire fuel system apart). – Pᴀᴜʟsᴛᴇʀ2♦ Oct 13 '17 at 13:46
  • @Pᴀᴜʟsᴛᴇʀ2 and, of course, where the pressure is being measured... – Solar Mike Oct 13 '17 at 13:49

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